Attenuated Salmonella typhimurium accumulated and multiplied preferentially in tumors as compared to in normal tissues after being injected intravenously into tumor-bearing mice and rats. VNP20009, an attenuated strain with msbB-purl- deletions, is being evaluated in Phase I trials in cancer patients. VNP20009 induced significant tumor growth inhibition in addition to accumulated to high levels in tumors. Some of the closely related strains, however, did not inhibit tumor growth although they accumulated to similar levels, as did VNP20009. The main goal for this proposal is to evaluate differential protein expression in two pairs of bacteria and to identify components that cause tumor growth inhibition by combining the proteomic and genomic approach. [unreadable] [unreadable] [unreadable]